Clutch, drive transmission device and image forming apparatus

Abstract

A clutch includes a rotatable inputting member, a rotatable outputting member, a stationary member, and a contact member. The outputting member includes an output contact portion. The contact member is positioned between the outputting member and the stationary member and includes an arcuate first contact surface and a second contact surface. When the input torque for rotating the inputting member is inputted, the outputting member and the contact member rotate in contact with the inputting member. When a reverse input torque for rotating the outputting member is inputted, the outputting member is spaced from the inputting member, and the output contact portion of the outputting member urges the first contact surface against the stationary member by urging the second contact surface of the contact member thereby to prevent rotation of the outputting member.

What is claimed is: 
     
       1. A clutch comprising:
 an inputting member rotatable by input of an input torque; 
 a rotatable outputting member to which the input torque is transmitted through said inputting member; 
 a stationary member including a cylindrical inner wall surface surrounding said inputting member and said outputting member and configured to be mounted on a mounting portion in a rotation prevented state; and 
 a contact member contactable to said inputting member, said outputting member and said stationary member, 
 wherein said outputting member includes an output contact portion contactable to an input engaging portion of said inputting member, 
 wherein said contact member is positioned between said outputting member and said stationary member and includes an arcuate first contact surface configured to contact the cylindrical inner wall surface of said stationary member and a second contact surface contactable to said output contact portion, 
 wherein when the input torque for rotating said inputting member in a rotational direction is inputted, said outputting member and said contact member rotate in contact with said inputting member, and 
 wherein when a reverse input torque for rotating said outputting member in the rotational direction is inputted, the input engaging portion of said inputting member and the output contact portion of said outputting member are spaced from each other, and said output contact portion of said outputting member urges the first contact surface against the cylindrical inner wall surface of said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member. 
 
     
     
       2. The clutch according to  claim 1 , wherein the first contact surface of said contact member has an arcuate shape, and
 wherein, when seen in a plane perpendicular to the axis of rotation of said inputting member and outputting member, an angle θ between a tangential line of the first contact surface at a position on an extended line connecting a rotation center of said outputting member and a contact portion where said output contact portion and the second contact surface contact each other, and the second contact surface including the contact portion is substantially equal to an angle θw between a tangential line of said output contact portion of said outputting member and a tangential line of the cylindrical inner wall surface of said stationary member at a position on an extended line connecting the rotation center of said outputting member to said output contact portion. 
 
     
     
       3. The clutch according to  claim 1 , wherein said contact member is provided in plurality and each of said contact members is held by a holding member. 
     
     
       4. The clutch according to  claim 3 , wherein said contact members include rotation contact portions, and the first contact surfaces of said contact members contact the cylindrical inner wall surface through contact of the respective rotation contact portions, and
 wherein said contact members are disposed at symmetrical positions with respect to the rotation center. 
 
     
     
       5. The clutch according to  claim 1 , wherein said outputting member includes an arcuate output portion slide contacting the cylindrical inner wall surface of said stationary member, and
 wherein said contact member includes a rotation contact portion contactable to said outputting member. 
 
     
     
       6. A clutch comprising:
 an inputting member rotatable by input of an input torque; 
 a rotatable outputting member to which the input torque is transmitted from said inputting member; 
 a stationary member including a cylindrical inner wall surface surrounding said inputting member and said outputting member and configured to be mounted on a mounting portion in a rotation prevented state; and 
 a contact member contactable to said inputting member, said outputting member and said stationary member, 
 wherein said outputting member includes an output contact portion contactable to an input engaging portion of said inputting member, 
 wherein said contact member is positioned between said outputting member and said stationary member and includes an arcuate first contact surface configured to contact the cylindrical inner wall surface of said stationary member and a second contact surface contactable to said output contact portion, 
 wherein when the input torque for rotating said inputting member in one rotational direction is inputted, said outputting member and said contact member rotate in the one rotational direction in contact with said inputting member, 
 wherein when a reverse input torque for rotating said outputting member in the one rotational direction is inputted, the input engaging portion of said inputting member and the output contact portion of said outputting member are spaced from each other, and said output contact portion of said outputting member urges the first contact surface against said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member in the one rotational direction, 
 wherein when the input torque for rotating said inputting member in the other rotational direction opposite to the one rotational direction is inputted, said outputting member and said contact member rotate in the other rotational direction in contact with said inputting member, and 
 wherein when a reverse input torque for rotating said outputting member in the other rotational direction is inputted, the input engaging portion of said inputting member and the output contact portion of said outputting member are spaced from each other, and said output contact portion of said outputting member urges the first contact surface against the cylindrical inner wall surface of said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member in the other rotational direction. 
 
     
     
       7. The clutch according to  claim 6 , wherein said inputting member includes an input engaging portion engageable with said outputting member and an input contact portion contactable to said contact member,
 wherein said output contact portion of said outputting member includes an output engaging portion engaging with said input engaging portion of said inputting member and a cam portion contactable to the second contact surface of said contact member, 
 wherein said contact member includes a driven portion contactable to said input contact portion of said inputting member, 
 wherein when said input engaging portion engages with said output engaging portion by the input torque for rotating said inputting member, the input torque from said inputting member is transmitted to said outputting member, and said cam portion of said outputting member and the second contact surface of said contact member are spaced from each other and said input contact portion of said inputting member drives said driven portion of said contact member, and 
 wherein when the reverse input torque for rotating said outputting member is inputted, said output engaging portion of said outputting member is spaced from said input engaging portion of said inputting member, and said cam portion of said outputting member urges said first contact surface against the cylindrical inner wall surface of said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member. 
 
     
     
       8. The clutch according to  claim 6 , wherein said contact member is provided at two positions so as to be symmetrically disposed with respect to a center of a rotational axis, and
 wherein said contact members include rotation contact portions contacting each other. 
 
     
     
       9. The clutch according to  claim 7 , wherein said outputting member includes an arcuate output portion slide contacting the cylindrical inner wall surface of said stationary member,
 wherein said contact member includes a rotation contact portion contactable to said outputting member, and 
 wherein when the reverse input torque is inputted:
 said input engaging portion of said inputting member and said output engaging portion of said outputting member are spaced from each other, 
 said contact member contacts said output contact portion of said outputting member and the cylindrical inner wall surface of said stationary member, 
 said arcuate output portion of said outputting member is urged against the cylindrical inner wall surface of said stationary member, and 
 rotation of said outputting member is locked by wedge action of said contact member thereby to block the reverse input torque with respect to two directions. 
 
 
     
     
       10. The clutch according to  claim 5 , wherein said arcuate output portion of said outputting member is provided with a plurality of groove portions. 
     
     
       11. A clutch comprising:
 an inputting member rotatable by input of an input torque; 
 a rotatable outputting member to which the input torque is transmitted from said inputting member; 
 a stationary member including a cylindrical inner wall surface surrounding said inputting member and said outputting member and configured to be mounted on a mounting portion in a rotation prevented state; and 
 a contact member contactable to said inputting member, said outputting member and said stationary member, 
 wherein said outputting member includes an output contact portion contactable to an input engaging portion of said inputting member, 
 wherein said contact member is positioned between said outputting member and said stationary member and includes an arcuate first contact surface configured to contact the cylindrical inner wall surface of said stationary member and a second contact surface contactable said output contact portion, 
 wherein when a rotational force with respect to one rotational direction is inputted to said inputting member, said outputting member and said contact member rotate in the one rotational direction in contact with said inputting member, 
 wherein when a rotational force for rotating said outputting member in the one rotational direction at a rotational speed faster than a rotational speed of said inputting member generates in said outputting member, the input engaging portion of said inputting member and the output contact portion of said outputting member are spaced from each other, and said output contact portion of said outputting member urges the first contact surface against said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member in the one rotational direction, 
 wherein when a rotational force with respect to the other rotational direction opposite to the one rotational direction is inputted to said inputting member, said outputting member and said contact member rotate in the other rotational direction in contact with said inputting member, and 
 wherein when a rotational force for rotating said outputting member in the other rotational direction at a rotational speed faster than a rotational speed of said inputting member generates in said outputting member, the input engaging portion of said inputting member and the output contact portion of said outputting member are spaced from each other, and said output contact portion of said outputting member urges the first contact surface against the cylindrical inner wall surface of said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member in the other rotational direction. 
 
     
     
       12. The clutch according to  claim 11 , further comprising an urging member configured to urge said contact member against said stationary member,
 wherein said inputting member includes an input contact portion contactable to said contact member, 
 wherein said contact member includes a driven portion contactable to said input contact portion of said contact member and is urged against said stationary member by said urging member, and 
 wherein when a rotational driving force is inputted to said inputting member, said input contact portion is contacted to said driven portion, and said contact member is rotated in the same direction as said inputting member while slide contacting the cylindrical inner wall surface of said stationary member. 
 
     
     
       13. The clutch according to  claim 1 , wherein the following relationship is satisfied:
   μ1+μ2>2 tan(θ w/ 2),
 
 where μ 1  is a friction coefficient in contact between said contact member and said stationary member, μ 2  is a friction coefficient in contact between said contact member and said outputting member, and θw is an angle between a tangential line of said output contact portion of said outputting member and a tangential line of the cylindrical inner wall surface of said stationary member at a position on an extended line connecting a center of a rotational axis of said outputting member to said output contact portion. 
 
     
     
       14. The clutch according to  claim 1 , wherein the first contact surface is provided with a plurality of groove portions which are in non contact with said stationary member. 
     
     
       15. The clutch according to  claim 1 , wherein said contact member is formed of a resin material. 
     
     
       16. The clutch according to  claim 1 , wherein said contact member is formed of a metallic material. 
     
     
       17. The clutch according to  claim 1 , wherein each of said inputting member, said outputting member and said stationary member is formed of a resin material. 
     
     
       18. The clutch according to  claim 1 , wherein when said clutch is seen on a plane perpendicular to a rotational axis of said inputting member, said input contact portion of said inputting member contactable to said outputting member is surrounded by said contact member. 
     
     
       19. The clutch according to  claim 1 , wherein an angle formed by a rectilinear line connecting a rotation center and one end of the first contact surface and a rectilinear line connecting the rotation center and the other end of the first contact surface is within a range from 60 degrees to 180 degrees. 
     
     
       20. The clutch according to  claim 1 , wherein said output contact portion of said outputting member has a helical shape. 
     
     
       21. The clutch according to  claim 20 , wherein said output contact portion of said outputting member has a logarithmic helical shape or an Archimedes helical shape. 
     
     
       22. The clutch according to  claim 14 , wherein the plurality of groove portions extend in a rotational axis direction. 
     
     
       23. A drive transmission device comprising:
 the clutch according to  claim 1 , wherein said clutch transmits an input torque from an inputting member to an outputting member, and when a reverse input torque inputted from said outputting member toward said inputting member, the reverse input torque is blocked; 
 a gear configured to transmit a driving force to said inputting member; and 
 a gear configured to transmit the driving force from said outputting member. 
 
     
     
       24. A image forming apparatus comprising:
 the drive transmission device according to  claim 23 , wherein said drive transmission device transmits the driving force to a cam member configured to space a press contacted roller pair; and 
 said cam member configured to space the roller pair.